Field of the Invention
The present invention relates to an electrode assembly and a plasma processing apparatus, and in particular relates to an electrode assembly having an electrode plate having gas-passing holes therein.
Description of the Related Art
Plasma processing apparatuses that carry out desired plasma processing on semiconductor device wafers as substrates have been known from hitherto. Such a plasma processing apparatus has a processing chamber in which a wafer is housed. A stage (hereinafter referred to as a “susceptor”) on which the wafer is mounted and that acts as a lower electrode, and an upper electrode that faces the susceptor are disposed in the processing chamber. Moreover, a radio frequency power source is connected to at least one of the stage and the upper electrode, so that radio frequency electrical power can be applied into a processing chamber inner space between the stage and the upper electrode.
In such a plasma processing apparatus, a processing gas supplied into the processing chamber inner space is turned into plasma by the radio frequency electrical power so as to produce ions and radicals, and the ions and radicals are led onto the wafer, whereby the wafer is subjected to the desired plasma processing, for example etching.
The upper electrode has an upper electrode plate that faces onto the processing chamber inner space, an electrode support having therein a buffer chamber into which a processing gas supplied in from the outside is introduced and which is open at a lower portion thereof, and a cooling plate that is interposed between the upper electrode plate and the electrode support and closes up the lower portion of the buffer chamber. Here, the upper electrode plate, the cooling plate, and the electrode support together constitute an electrode assembly. The upper electrode plate and the cooling plate each have therein a plurality of gas-passing holes penetrating therethrough. In the upper electrode, the gas-passing holes in the upper electrode plate communicate with the gas-passing holes in the cooling plate, and the communicated gas-passing holes lead the processing gas from the buffer chamber into the processing chamber inner space.
With a conventional plasma processing apparatus, upon the desired plasma processing being carried out repeatedly on wafers, the upper electrode plate is worn down by the ions and so on, and hence the gas-passing holes in the upper electrode plate become enlarged. Moreover, the gas-passing holes in the upper electrode plate and the gas-passing holes in the cooling plate are disposed collinearly with one another. As a result, when the desired plasma processing is carried out on a wafer, ions produced in the processing chamber inner space may flow back through the gas-passing holes in the upper electrode plate, and thus infiltrate into the gas-passing holes in the cooling plate. The upper electrode plate is made of semiconductor silicon (Si), but the cooling plate is made of aluminum (Al), which is a conductor, and hence there has been a problem of abnormal electrical discharges occurring due to ions that have infiltrated into the gas-passing holes in the cooling plate, whereby the upper electrode plate is damaged.
In recent years, cylindrical embedded members that are inserted into the gas-passing holes in the upper electrode plate have thus been developed. Each of the embedded members has a spiral groove formed in an outer peripheral surface thereof; ions that flow back through a gas-passing hole in the upper electrode plate and infiltrate into the groove collide with a wall of the groove so that the ions lose energy, whereby the ions are prevented from infiltrating into the gas-passing holes in the cooling plate and hence the upper electrode plate is prevented from being damaged (see, for example, Japanese Laid-open Patent Publication (Kokai) No. 2004-356531).
However, in the case of using the above embedded members in a plasma processing apparatus, because there are many gas-passing holes in the upper electrode plate, many embedded members are required, and hence there is a problem that this leads to an increase in the number of parts.
Moreover, the embedded members are worn away through collisions with ions, and hence must be replaced at predetermined replacement intervals. Because many embedded members are required in the plasma processing apparatus as described above, the replacement work is troublesome, and hence there is a problem that the ability to carry out maintenance worsens.